Operators are expected to handle, store, transport and apply pesticides in various types of formulations. Understanding the properties of each is critical to preparing and using them correctly and for achieving the best efficacy.
Many concentrate pesticides are formulated into products that need to be added to water, as a carrier, to make a finished spray mix that can applied in the field. In general, these can be formulated as either a solution, an emulsion or a suspension.
The amount of active ingredient in a product is always given on the label, for example a 10kg pack of a 72% w/w water soluble granule glyphosate product contains 72% by weight of active ingredient – or 7.2kg of active ingredient and 2.8kg of inert ingredient.
Soluble formulations
Concentrate pesticide formulations containing soluble active ingredients, such as salts, include soluble concentrates (SC), water soluble powders (SP) and water-soluble granules (SG). Glyphosate is a good example of active ingredient of this type.
Soluble active ingredients in these formulations will dissolve readily in water. This means it is relatively easy to get a uniform solution, and this can be achieved with little or no agitation in the sprayer.
Thanks to being dissolved, these formulation types rarely cause problems with blocked filters and they are unlikely to cause sprayer parts to wear. They are, in general, fairly non-flammable and have low toxicity. While this makes them a good formulation option, the number of products is limited.
During filling and handling operators need to take care soluble formulations do not contaminate water, via drains or when applying near watercourses. This is crucial because it’s difficult to remove the dissolved active ingredient from the water.
Soluble powders (SP) and granules (SG) must be kept dry – so must be stored above liquids.
Take care during filling to ensure partially solubilised residues of powders and granules do not remain and risk contaminating filling points, such induction hoppers and tank lids. Also remember that when adding these to the sprayer they need to be given time to absorb water and disperse in the sprayer.
Emulsifiable concentrates
A wide range of products are formulated and sold in emulsifiable concentrate (EC) formulations. These are formed by mixing an oil-soluble active ingredient with an oil-based solvent and a mixing agent, which allows the product to be mixed with water to form an emulsion.
Emulsifiable concentrates are complex and expensive to manufacture. They are, however, quite straightforward for operators to pour and mix, require significantly less agitation than suspension formulations and are not likely to block nozzles and filters.
Suspension formulations
A suspension is also a liquid mixture, which is formed by dispersing fine solid particles in a liquid. Unlike a solution, these particles do not dissolve in the liquid carrier and mixtures must be constantly agitated to maintain a uniform particle distribution in sprayer tanks.
Different types of suspension formulations are commonly used to facilitate the safe and effective application of active ingredients. These are either supplied as dry or liquid concentrate formulations, which operators need to dilute.
Water Dispersible Granules must be constantly agitated to ensure uniform distribution in sprayer tanks. When filling operators should check induction hopper edges for deposits to ensure no cross contamination of products.
Dry formulation types include wettable powders (WP) and water dispersible granules (WDG).
Wettable powders
Wettable powder formulations contain an active ingredient mixed with a dry carrier. These are then milled down to a fine powder to reduce particle size to a fineness. This enables the dispersed product to be applied without clogging filters or nozzles.
A major disadvantage of wettable powders is that the concentrate product is dusty and this makes it liable to waft around – particularly up at the operator. The problem is made worse because the fine powder doesn’t pour easily for measuring and this means operators need to scoop it out of the packaging.
It’s recommended operators pre-mix the required amount of wettable powder product before adding it to the sprayer. Use a small amount of water to form a paste and then add more water to further bulk out the mix. Mixing containers should then be rinsed into the sprayer.
Water soluble packs
To address the problem of handling wettable powders manufacturers may supply products as water soluble packages, which can be added directly to water.
Add water soluble packs to the sprayer at the beginning of the filling sequence, to allow time to mix and wear dry gloves when handling these packages.
Water dispersible granules
Water dispersible granules are similar to wettable powders, except they comprise larger particles and are much less dusty. This enables them to be poured out of packaging more easily than powders.
Although many granules are supplied with a specific measuring vessel for the product, these can vary in accuracy by +/- 10% and are not particularly accurate. It’s also important to use this only for that specific product and no other. This is because granular products’ bulk density can vary significantly.
A far better, more accurate way to measure granules is by weight. This is particularly important for highly concentrated actives, which are applied in very low doses from 42gm/ha and even down to 6gm/ha in 1,000 litres of water.
As with wettable powder products, the required amount should be mixed with a small amount of water before being added to the sprayer. They must also be given time to disperse and require constant agitation – to ensure filters and nozzles are not blocked by undispersed product.
Liquid suspension formulations
Suspension type formulations can also be supplied in a liquid form. Suspension concentrates, sometimes called ‘flowables’, contain particles of active ingredients suspended in a liquid.
These liquid suspensions overcome many of the dust hazard and measuring problems associated with wettable powders and water dispersible granules.
They do, however, tend to be more chemically more complex, because they require suspension agents to keep the solids from settling in the packaging. Also wetting agents are usually needed to keep the solid surfaces wetted in water.
Active ingredient concentrations in flowables are often lower than those found in solution formulation types. As with all suspensions it is crucial to maintain agitation when diluted to prevent them settling to the bottom of the tank.
Also ensure air doesn’t get into the system because this can lead to foaming in the tank.
Suspo-emulsions
Suspension concentrates and emulsion formulations can also be mixed together into suspo-emulsion products (SE). As with any suspension formulation these also require sufficient agitation after dilution to prevent solid particles settling out in sprayer tanks.
Shake Suspo-emulsion products before opening to help pouring and ensure no solid particles have settled out in containers.
Take care when mixing suspo-emulsions with emulsions in tank mixes. This is because the solid particle can penetrate the oil droplets of the emulsifiable concentrate (EC) and lead to particles clumping.
When either is applied alone this is not likely to be a problem, but care is needed when choosing other tank mix partners.
Safe mixing procedure
It’s not difficult to effectively mix products, provided operators follow the information given on the product label and follow a few basic mixing principles. The best way to avoid any potential is to always follow the AIC Tank Mixing Sequence.
Always read the labels – before starting. They will contain sections on mixing, filling and compatibility. Never add more than one product at time into the sprayer.
It is also vital to add products to the sprayer in the correct order and manner. This is crucial to ensure each is properly dispersed within the water and enables the pesticide to work correctly and to avoid blocked filters and/or nozzles.
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